/****************************************************************************
 *
 * Copyright 2016 Samsung Electronics All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
 * either express or implied. See the License for the specific
 * language governing permissions and limitations under the License.
 *
 ****************************************************************************/
/************************************************************************
 * libc/math/lib_libexpi.c
 *
 * This file is a part of NuttX:
 *
 *   Copyright (C) 2012 Gregory Nutt. All rights reserved.
 *   Ported by: Darcy Gong
 *
 * It derives from the Rhombs OS math library by Nick Johnson which has
 * a compatibile, MIT-style license:
 *
 * Copyright (C) 2009-2011 Nick Johnson <nickbjohnson4224 at gmail.com>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 ************************************************************************/

/************************************************************************
 * Included Files
 ************************************************************************/

#include <sys/types.h>
#include <math.h>

/************************************************************************
 * Public Functions
 ************************************************************************/

/************************************************************************
 * Pre-processor Definitions
 ************************************************************************/

#define M_E2    (M_E * M_E)
#define M_E4    (M_E2 * M_E2)
#define M_E8    (M_E4 * M_E4)
#define M_E16   (M_E8 * M_E8)
#define M_E32   (M_E16 * M_E16)
#define M_E64   (M_E32 * M_E32)
#define M_E128  (M_E64 * M_E64)
#define M_E256  (M_E128 * M_E128)
#define M_E512  (M_E256 * M_E256)
#define M_E1024 (M_E512 * M_E512)

/************************************************************************
 * Private Data
 ************************************************************************/

static double _expi_square_tbl[11] = {
	M_E,						/* e^1 */
	M_E2,						/* e^2 */
	M_E4,						/* e^4 */
	M_E8,						/* e^8 */
	M_E16,						/* e^16 */
	M_E32,						/* e^32 */
	M_E64,						/* e^64 */
	M_E128,						/* e^128 */
	M_E256,						/* e^256 */
	M_E512,						/* e^512 */
	M_E1024,					/* e^1024 */
};

/************************************************************************
 * Public Functions
 ************************************************************************/

double lib_expi(size_t n)
{
	size_t i;
	double val;

	if (n > 1024) {
		return INFINITY;
	}

	val = 1.0;

	for (i = 0; n; i++) {
		if (n & (1 << i)) {
			n &= ~(1 << i);
			val *= _expi_square_tbl[i];
		}
	}

	return val;
}
